From the U.S. Geological Survey today:
In a study of 13 hydraulically fractured shale gas wells in north-central Pennsylvania, USGS researchers found that the microbiology and organic chemistry of the produced waters varied widely from well to well.
The variations in these aspects of the wells followed no discernible spatial or geological pattern but may be linked to the time a well was in production. Further, the study highlighted the presence of some organic compounds (e.g. benzene) in produced waters that could present potential risks to human health, if the waters are not properly managed.